Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/build.yml

@@ -34,7 +34,7 @@ jobs:
     if: needs.release-check.outputs.is-release != ''
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Install nix
       uses: cachix/install-nix-action@v31
       with:
@@ -65,7 +65,7 @@ jobs:
     if: needs.release-check.outputs.is-release != ''
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Make addpkg script executable
       run: chmod +x ./addpkg.sh
     - name: Execute addpkg.sh to update nix package's catalog